This invention relates broadly to support tooling for a workpiece, and more particularly, pertains to a fluid pressure-actuated, spring-return expandable mandrel for instantaneously gripping a workpiece during a machining process.
A variety of tooling devices and designs have been employed for use as work supports to retain workpieces in a stable position during machining or other manufacturing operations on the workpiece. Such support tooling is important in applications where the workpiece must support accurate centering and level support. For example, the design of support tooling is critical in the machining of transmission plates, motorcycle engine covers and various other engine components.
One type of known workpiece support tooling is disclosed in U.S. Pat. No. 4,932,642, issued Jun. 12, 1990 to Salenbien et al. The support tooling of this device includes a spring-loaded sleeve member designed to engage the workpiece at a specific contact point about the shaft or bore of the workpiece. The weight of the workpiece drives the sleeve member to a second location, thereby causing a plurality of ball bearing members to move radially and engage the bore or shaft of the workpiece at a second point of contact. Because this device is dependent upon the disposition and removal of the workpiece, there are drawbacks in the amount of friction between the components, and in the desired responsiveness and positive gripping ability of the support tooling.
Many workpiece holders are clamping devices of one kind or another which rely on fluid pressure (hydraulic or pneumatic) to engage and disengage a workpiece under load. All of the clamping devices presently on the market suffer from at least some of the following disadvantages. These devices comprise a large number of parts having such exposed positions that they become sensitive to fouling and wear. In connection with machining, there is also a danger that cuttings may assemble on the different parts and prevent correct clamping. These devices also require a great deal of space and are often difficult to install and very expensive to manufacture. In addition, these devices operate with high friction levels which negatively effect the responsiveness of the workpiece holder and the efficiency of the machining process.
In order to maintain the integrity of the machining operations and avoid damage to workpieces, any workpiece holder used to maintain the workpiece in position should not readily slip, breakdown or excessively wear under significant loads typical to uses of such supports. Existing work support tooling suffers from one or more of these problems. Sometimes a problem manifests itself through slippage of the work support components causing loss of stable positioning and potential injury to workers. Other times, there may be unexpected physical failure of the work support and resulting change to the workpiece for interruption of machining operations.
Prior to the present invention, it is believed there has not been a reliable workpiece support of a simple, compact design that minimizes friction and utilizes a relatively small number of parts to provide optimum support and positive gripping of a workpiece using a reasonable amount of fluid pressure.
In addition, it has been difficult to achieve a workpiece holding system which grips one or more bores formed in the workpiece by means of an expandable structure having a reaction time which is substantially equal to its release time so as to improve the efficiency of the machining of the gripped workpiece.
Thus, it can be seen that a need exists for a workpiece holder and, more particularly, an expandable and retractable structure which will enable a quick change support and gripping apparatus capable of providing a desired leveling and centering of the workpiece.
It is one object of the present invention to provide a workpiece holder which, as far as possible, eliminates the above shortcomings of previously known workpiece supports and clamping devices, and which also make it possible to perform a highly efficient and precise gripping of the workpiece.
It is another object of the present invention to provide an expandable mandrel useful as a workpiece support whereby a gripping relationship may be reliably created and released with substantially reduced friction by selective application of relatively low fluid pressure and a biasing arrangement, respectively.
It is also an object of the present invention to provide a workpiece support structure having an expandable grip post with a tip which facilitates self-centering in relatively small bores formed in the workpiece.
It is a further object of the present invention to provide a workpiece holder whereby equal pressure is selectively applied to a plurality of expandable gripping sections.
It is an additional object of the present invention to provide a workpiece holder having an assembly which is interchangeable with variously-sized, expandable grip posts.
In one aspect of the invention, a workpiece holder includes a grip post having an interior wall structure and an exterior wall structure defining a plurality of expandable sections adapted to engage the wall of a bore formed on a workpiece. The grip post has a cam arrangement abutting the interior wall structure. A pin arrangement is movably mounted in the grip post and has a tapered head engageable with a cam arrangement. A system is provided for instantaneously imparting longitudinal movement to the pin arrangement whereby the exterior wall structure of the grip post is expanded into gripping relationship with the workpiece by the progressive engagement of the tapered head with the cam arrangement. The workpiece holder also includes a base assembly comprised of a base having a fluid passageway formed therein in communication with a source of fluid pressure, a cap joined to the base and formed with a central through hole for receiving the pin arrangement and a gland sealably interposed between the base and the cap and provided with a bore for receiving the pin arrangement. The bore is in aligned communication with the fluid passageway and through hole. The base assembly is adapted to be coupled to a manifold through which fluid pressure is delivered. The exterior wall structure of the grip post includes an upper portion having a nose-cone shape with a cylindrical tip, a middle portion of cylindrical configuration and a radially-enlarged lower portion of cylindrical contour. The expandable sections are formed by a set of cut lines spaced equidistantly from one another and extending from the tip to the lower portion of the grip post. The cap includes a threaded neck which surrounds the lower portion of the grip post and the grip post is coupled to the base assembly by a nut which is threadably received on the threaded neck. The interior wall structure forms a central chamber for accommodating a retainer having a top, a sidewall depending from the top, and a central opening extending along a longitudinal axis. A plurality of windows is formed in the sidewall and spaced equidistantly relative to the longitudinal axis. The windows form races for retaining the cam arrangement in the form of ball bearing components maintained in position by coil springs acting between the bearing components and the top of the retainer. The interior wall structure also includes a series of horizontally-disposed, threaded openings extending generally perpendicular to the longitudinal axis for receiving a set of screws passing through the exterior wall structure and the interior wall structure of the grip post for maintaining the retainer in an upper portion of the central chamber. The pin arrangement includes an elongated, cylindrical pin having a frusto-conically shaped head with a tip, the cylindrical pin having a first portion with a first diameter and a second portion having a second diameter less than the first portion diameter. The pin arrangement further includes a piston having a cylindrical body movably and sealably disposed in the bore of the gland, and a hat-shaped seat formed with a central pocket for holding a centering ball upon which the pin arrangement is supported. The seat includes an upstanding crown and a radially-enlarged rim having a bottom surface which is engageable with the gland, and a top surface for supporting the lower end of a wave spring that surrounds the crown and has an upper end engaged with the cap. The tapered head of the pin arrangement has a diameter progressively tapering toward the tip. The pin arrangement is axially slidable within the central opening formed in the retainer. The system for instantaneously imparting longitudinal movement to the pin arrangement is comprised of a fluid pressure source. In the preferred embodiment, the grip post has three equidistantly-spaced, expandable sections. A first set of fasteners is provided for joining the base and the cap together, while a second set of fasteners is provided for joining the base, the cap and the manifold together. The tip of the grip post is preferably provided with serrations to facilitate the gripping of the workpiece.
In another aspect of the invention, an expandable mandrel includes a base assembly having a fluid passageway in communication with a source of fluid pressure. A grip post has a plurality of expandable sections adapted to engage the wall of a bore formed on a workpiece and a central chamber having an interior wall for accommodating a retainer formed of a series of races, each race provided with a first resilient device for retaining a bearing component therein. A movable pin arrangement has an upper, tapered end engageable with the bearing components and a lower end supported in communication with the fluid passageway and surrounded by a second resilient device. When the wall defining the bore of the workpiece is positioned upon the grip post, fluid pressure delivered to the passageway will force the pin arrangement axially against the force of the second resilient device, whereby the tapered end of the pin arrangement deforms each first resilient device and forces the bearing components radially outward from the races against the interior wall of the central chamber causing the grip post sections to expand against the workpiece bore wall so that the workpiece is positively supported and gripped. Upon release of the fluid pressure from the passageway, each first resilient device and the second resilient device will return the pin arrangement in the opposite axial direction withdrawing the tapered end of the pin arrangement, so that each bearing component is forced back into its respective race by its first resilient device causing the grip sections to retract from the workpiece to instantaneously release the workpiece.
In yet another aspect of the invention, a workpiece holder has a plurality of components disposed in respective races engageable with a tapered end of an elongated member. The improvement resides in a system for supplying and regulating fluid pressure in the workpiece holder such that, upon application of fluid pressure, the elongated member moves axially in one direction so as to force the bearing components out of the races to enable the workpiece to be gripped on the holder. A resilient arrangement in the workpiece holder is operable upon release of fluid pressure to move the elongated member axially in the opposite direction so as to return the bearing components to their races to enable the workpiece to be released from the holder.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.